Method for manufacture of reflecting mirror, reflecting mirror, illumination device, and projector

ABSTRACT

An auxiliary reflecting mirror is manufactured by heating the central portion of a quartz glass tube and compressing the central portion by pushing two end portions of the quartz glass tube so that the wall thickness of the central portion thickens, accommodating the quartz glass tube after thickening the wall thickness of the central portion in a mold having inner surfaces formed to the reflecting surface shape, which is to be formed in an auxiliary reflecting mirror, and forming an expanded portion by expanding the central portion, of which the wall thickness was thickened, by introducing a gas from the two ends of the quartz glass tube, cutting the quartz glass tube in at least the central portion of the expanded portion, evaporating a reflecting film on the outer surface of the expanded portion and forming a reflecting surface.

BACKGROUND

Exemplary aspects of the present invention relate to a method for themanufacture of an auxiliary reflecting mirror for installation in anillumination device, an auxiliary reflecting mirror manufactured by sucha manufacturing method, an illumination device equipped with such anauxiliary reflecting mirror, and a projector equipped with such anillumination device.

Prior Art

A related art illumination device is equipped with: a light-emittingtube and a main reflecting mirror to direct the light emitted from thelight-emitting tube in a prescribed direction; and an auxiliaryreflecting mirror composed of quartz or the like provided in a positionfacing the main reflecting mirror on the other side of thelight-emitting tube. Thus, it was possible to utilize effectively thelight that was emitted from the light-emitting tube. However, a straylight was not supplied for use. See JP-A-H8-31382 (second page, FIG. 1).

SUMMARY

In the illumination device of this type, because the auxiliaryreflecting mirror was provided with the object of increasing the lighteffective efficiency, a high accuracy was required for the reflectingsurface thereof.

Exemplary aspects of the present invention address this and/or otherproblems and provide: a method for the manufacture of a reflectingmirror, which makes it possible to form the reflecting surface with goodaccuracy and with a high light utilization efficiency; the reflectingmirror manufactured by such a method; an illumination device equippedwith such a reflecting mirror, and a projector equipped with such anillumination device.

A method for the manufacture of a reflecting mirror in accordance withan exemplary aspect of the present invention is a method for themanufacture of a reflecting mirror of an illumination device including alight-emitting tube and the reflecting mirror to reflect a light fromthe light-emitting tube. This method includes heating the centralportion of a quartz glass tube and compressing the central portion bypushing the two end portions of the quartz glass tube so that the wallthickness of the central portion thickens, accommodating the quartzglass tube after thickening the wall thickness of the central portion ina mold having an inner surface formed to the reflecting surface shapewhich is to be formed in a reflecting mirror, and forming an expandedportion by expanding the central portion, of which the wall thicknesswas thickened, by introducing a gas from the two ends of the quartzglass tube, cutting the quartz glass tube in at least the centralportion of the expanded portion, and evaporating a reflecting film onthe outer surface of the expanded portion and forming a reflectingsurface.

With such a method, the reflecting surface can be formed with goodaccuracy and an auxiliary reflecting mirror with a high lightutilization efficiency can be manufactured.

Further, in a method for the manufacture of a reflecting mirror inaccordance with an exemplary aspect of the present invention, in thecutting, both end portions of the cylindrical portions extendingoutwardly from the two ends of the expanded portion are cut in additionto cutting in the vicinity of the central portion of the expandedportion of the quartz glass tube, and cylindrical mounting supportportions provided to fix to the light-emitting tube are formed.

Because the mounting support portions are thus formed, an auxiliaryreflecting mirror with good mounting ability on the light-emitting tubecan be manufactured.

Further a reflecting mirror in accordance with an exemplary aspect ofthe present invention is manufactured by the above-described method forthe manufacture of a reflecting mirror.

The reflecting mirror thus manufactured has a high light utilizationefficiency and good mounting ability on the light-emitting tube.

Further, an illumination device in accordance with an exemplary aspectof the present invention includes a light-emitting tube and a reflectingmirror to reflect the light from the light-emitting tube toward anillumination region. The reflecting mirror is manufactured by theabove-described method for the manufacture of a reflecting mirror.

Because the reflecting mirror manufactured by the above-describedmanufacturing method is provided, an illumination device with a highlight utilization efficiency can be obtained.

Further, an illumination device in accordance with an exemplary aspectof the present invention includes a light-emitting tube, a mainreflecting mirror to reflect the light from the light-emitting tubetoward an illumination region, and an auxiliary reflecting mirror toreflect the light from the light-emitting tube toward the mainreflecting mirror. The auxiliary reflecting mirror is manufactured bythe above-described method for the manufacture of a reflecting mirror.

Because the auxiliary reflecting mirror manufactured by theabove-described manufacturing method is provided, an illumination devicewith a high light utilization efficiency can be obtained.

Further, a projector in accordance with an exemplary aspect of thepresent invention includes the above-described illumination device, alight modulation device to modulate the luminous flux emitted from theillumination device according to an image information, and a projectionoptical system to project the luminous flux modulated by the lightmodulation device.

Because the above-described illumination device is provided, a projectorwith increased luminosity can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) are schematics of an illumination device equippedwith an auxiliary reflecting mirror of an exemplary embodiment of thepresent invention;

FIG. 2 is a process flow diagram illustrating the method for themanufacture of an auxiliary reflecting mirror;

FIG. 3 is a schematic illustrating the process for the manufacture of anauxiliary reflecting mirror;

FIG. 4 is an optical path comparison schematic for the inner surfacereflection and outer surface reflection;

FIG. 5 is a schematic illustrating the comparison results obtained inthe case inner surface reflection and outer surface reflection; and

FIG. 6 is a schematic of the projector equipped with the illuminationdevice of the aforementioned embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

First, prior to explaining a method for the manufacture of a reflectingmirror of an exemplary embodiment of the present invention, anillumination device including an auxiliary reflecting mirrormanufactured by this manufacturing method will be explained.

FIG. 1(a) is a schematic of an illumination device including anauxiliary reflecting mirror manufactured by the method for themanufacture of a reflecting mirror in accordance with an exemplaryaspect of the present invention.

This illumination device 100 includes a light-emitting tube 10, a mainreflecting mirror 20 to reflect the light from the light-emitting tube10 toward the illumination region, and an auxiliary reflecting mirror 30to reflect the light from the light-emitting tube 10 toward the mainreflecting mirror 20. The light-emitting tube 10 is made from quartzglass or the like and is composed of a central light-emitting portion 11having sealed inside thereof tungsten electrodes 12, 12, mercury, a raregas, and a small amount of a halogen, and sealing portions 13, 13 onboth sides of the light-emitting portion 11. A metal foil 14 composed ofmolybdenum and connected to the electrode 12 is sealed hermetically ineach sealing portion 13. Each metal foil 14, 14 is provided withrespective lead wire 15, 15 leading to the outside. The light-emittingtube 10 is not limited to a mercury lamp and may be a metal halide lampor a xenon lamp.

The main reflecting mirror 20 is a reflecting element disposed behindthe light-emitting portion 11 and includes a reflecting portion having aconcave reflecting surface shaped as an ellipsoid of rotation and athrough hole 21 to fix the light-emitting tube 10. The through hole 21is located in the central portion of the reflecting portion. Thelight-emitting tube 10 is fixed with an inorganic adhesive 22, such as acement, in the through hole 21 of the main reflecting mirror 20 so thatthe axis of the light-emitting tube 10 and the axis of the mainreflecting mirror 20 coincide with each other and that the arc imagegenerated between a pair of electrodes 12 and the first focal point ofthe main reflecting mirror 20 coincide with each other.

The auxiliary reflecting mirror 30 is a reflecting element disposed infront of the light-emitting portion 11 and is fabricated by using, forexample, quartz or Neoceram, which is a material with a low thermalexpansion, or transparent alumina, sapphire, quartz, fluorite, or YAGwhich are the materials with a high thermal conductivity. The auxiliaryreflecting mirror 30 includes a concave portion 31 having a reflectingsurface 32 and enclosing almost half of the front side of thelight-emitting portion 11 and a mounting support portion 35 extendingoutwardly from the central portion of the concave portion 31 andprovided to fix to the light-emitting tube 10. Because the outer surface33 of the concave portion 31 is molded to the prescribed surface shapewith a better accuracy than the inner surface 34 due to themanufacturing process thereof, this being described in detail below, areflecting surface 32 is formed on the outer surface 33. The auxiliaryreflecting mirror 30 of such a configuration is inserted into themounting support portion 35 so that the axis of the sealing portion 13of the light-emitting tube 10 coincides with the axis of the auxiliaryreflecting mirror 30. The focal point of the reflecting surface 32 ismade to coincide with the arc image generated between the pair ofelectrodes 12. An inorganic adhesive 40, such as a cement, is injectedinto a gap between the inner periphery of the mounting support portion35. The outer periphery of the sealing portion, and the auxiliaryreflecting mirror is fixed to the light-emitting tube 10.

The luminous flux emitted from the illumination device 100 will beexplained in detail herein with reference to FIG. 1(b). Of the luminousflux emitted from the arc image generated between the pair of electrodes12 of the light-emitting portion 11, a luminous flux B1 that wasdirected straight to the main reflecting mirror 20 is reflected by thereflecting surface of the main reflecting mirror 20 and outgoes towardthe position of a second focal point F2.

Further, a luminous flux B2 emitted from the arc image generated betweenthe pair of electrodes 12 of the light-emitting portion 11 in thedirection opposite the main reflecting mirror 20 is reflected by thereflecting surface 32 of the auxiliary reflecting mirror 30 toward themain reflecting mirror 20, then reflected by the reflecting surface ofthe main reflecting mirror 20, and outgoes from the main reflectingmirror 20 so as to be converged toward the position of the second focalpoint F2.

In a related art illumination device that was not equipped with theauxiliary reflecting mirror 30, the luminous flux emitted from thelight-emitting portion 11 had to be converged in the position of thesecond focal point F2 only with the main reflecting mirror and theaperture diameter of the reflecting surface of the main reflectingmirror had to be increased.

However, providing the auxiliary reflecting mirror 30 makes it possibleto reflect the luminous flux that is emitted from the light-emittingportion 11 in the direction (forward) opposite to the main reflectingmirror 20 with the auxiliary reflecting mirror 30 so that it falls onthe reflecting surface of the main reflecting mirror 20. Therefore,almost the entire luminous flux emitted from the light-emitting portion11 can be converged to a fixed point and emitted even if the aperturediameter of the reflecting surface of the main reflecting mirror 20 issmall, and the size of the main reflecting mirror 20 in the optical axisdirection and the aperture diameter thereof can be decreased. Thus, theillumination device 100 can be miniaturized and the inner layout of anelectronic device, for example, a projector incorporating theillumination device 100 is facilitated.

Further, providing the auxiliary reflecting mirror 30 decreases thelight gathering spot diameter in the second focal point F2. Therefore,even if the distance between the first focal point F1 and second focalpoint F2 of the main reflecting mirror 20 is decreased, almost theentire light emitted from the light-emitting portion 11 can be gatheredby the main reflecting mirror 20 and auxiliary reflecting mirror 30 inthe second focal point and used, and the light utilization efficiencycan be greatly increased.

As described hereinabove, because the auxiliary reflecting mirror 30 isused, the luminous flux emitted from the light-emitting portion 11 inthe direction (forward) opposite to the main reflecting mirror 20 isconverged in the position of the second focal point F2 of the mainreflecting mirror 20 similarly to the luminous flux directly fallingfrom the light-emitting portion 11 on the reflecting surface of the mainreflecting mirror 20, thereby increasing the light utilizationefficiency of the illumination device 100. Therefore, the auxiliaryreflecting mirror 30 having the reflecting surface 32 with a bettermolding accuracy makes it possible to construct the illumination device100 in which the effect of installing the auxiliary reflecting mirror 30can be demonstrated to even greater degree.

A method for the manufacture of the auxiliary reflecting mirror 30 willbe described below.

FIG. 2 and FIG. 3 show a process flow diagram and process modelschematic explaining the method for the manufacture of the auxiliaryreflecting mirror of one exemplary embodiment of the present invention,and the explanation will be conducted following those diagrams.

First, the central portion of, for example, quartz glass tube 6, whichis a starting material, is heated to the prescribed high temperature andmade to be easily deformable (S1 in FIG. 2 and FIG. 3, referred tohereinbelow as a heating step).

Then, the two end portions of the quartz glass tube 6 are pushed andcompressed in the central direction to cause bulging in the centralportion 6 a (S2 in FIG. 2 and FIG. 3, referred to hereinbelow as abulging step). In other words, the central portion 6 a is compressed bypushing the two end portions of the quartz glass tube 6 so that the wallthickness of the central portion 6 a thickens.

Then the bulged quartz glass tube 6 (the central portion 6 a having thethickened wall thickness) is accommodated in a molding mold 80 and inthis state blow molding is conducted by pumping a gas (inert gas or air)from the two end portions of the quartz glass tube 6 and the bulgedcentral portion 6 a (the central portion 6 a having the thickened wallthickness) is expanded and an expanded portion 6 b is formed (S3 in FIG.2 and FIG. 3, referred to hereinbelow as an expansion step). As aresult, an integrated body is formed which is composed of the hollowexpanded portion 6 b and cylindrical portions 6 c extending outwardlyfrom both ends thereof. Here, the upper mold 81 and lower mold 82 of themolding mold 80 have the inner surfaces 81 a, 82 a formed to a shapewhich is ideal as a shape of the reflecting surface 32, which is to beformed in the auxiliary reflecting mirror 30. Because the centralportion 6 a is expanded in a state of accommodation inside the moldingmold 80, the ideal reflecting surface shape is transferred onto theouter surface 33 of the expanded portion 6 b. Because the gas is blownonto the inner surface 34 of the expanded portion 6 b in the expansionstep, this inner surface is difficult to form to the desired reflectingsurface shape.

Then, the quartz glass tube 6 is cut in two in the vicinity of thecenter of the expanded portion 6 b thereof and both end portions of thecylindrical portions 6 c extending outwardly from the two ends of theexpanded portion 6 b are cut off (S4 in FIG. 2 and FIG. 3, referred tohereinbelow as a cutting step). As a result, an auxiliary reflectingmirror body is formed which is composed of a concave portion 31 havingan almost semispherical concave surface and a mounting support portion35 extending outwardly from the central portion of the concave portion31.

Then, a reflecting surface 32 is formed by evaporating a reflecting filmby sputtering or the like on the outer surface 33 of the concave portion31, which had, as described hereinabove, a high accuracy as the surfaceto form the reflecting surface (S5 in FIG. 2 and FIG. 3, referred tohereinbelow as a evaporation step). As a result, the reflecting surface32 becomes a reflecting surface capable of reflecting with goodefficiency the light from the light-emitting tube 10 toward the mainreflecting mirror 20.

Thus, with the present exemplary embodiment, the reflecting surface 32was formed on the outer surface 33 side of the concave portion 31 ontowhich the ideal reflecting surface shape provided on the molding mold 80was transferred. Therefore, the reflecting surface 32 can be formed withgood accuracy and it is possible to obtain the auxiliary reflectingmirror 30 with a high light utilization efficiency, which is capable ofreflecting with good efficiency the light from the light-emitting tube10 toward the main reflecting mirror 20. As a consequence, theillumination device 100 with a high light utilization efficiency can beobtained.

Furthermore, because the auxiliary reflecting mirror 30 has the mountingsupport portion 35, mounting on the light-emitting tube 10 isfacilitated as compared with the configuration including only theconcave portion 31, without the mounting support portion 35. Further,the mounting support portion 35 is effective from the standpoint ofmounting ability, but the present invention is not necessarily limitedto the configuration including the mounting support portion 35.

The illumination device 100 in accordance with an exemplary aspect ofthe present invention is not limited to the above-described exemplaryembodiment and can be implemented in a variety of modes, withoutdeparting from the essence thereof. For example, the followingmodifications are also possible.

In the present exemplary embodiment, an example was described in whichthe expanded portion 6 b was cut in the central portion and then thereflecting surface 32 was formed by vapor depositing the reflecting filmon the outer surface of the concave portion 31. However, it is alsopossible to conduct vapor deposition of the reflecting film on the outersurface of the expanded portion 6 b prior to cutting and then conductcutting in the central portion thereof.

Furthermore, in the present exemplary embodiment, a method for themanufacture of the auxiliary reflecting mirror 30 was explained. But themain reflecting mirror 20 also may be manufactured by a similarmanufacturing method.

Further, it was mentioned hereinabove, that because the gas is blownonto the inner surface 34 of the expanded portion 6 b in the expansionstep, this inner surface is difficult to form to the desired reflectingsurface shape. Here, optical paths of reflected light will be comparedto the case where the reflecting surface 32 was formed on the innersurface 34 and the case of the present example where the reflectingsurface was formed on the outer surface 33. The effect attained byforming the reflecting surface on the outer surface 33 will be verified.In the case of reflection from the outer surface 33, the results areaffected by the refractive action of the light-emitting tube 10. Forthis reason, the comparison of optical paths will be conducted by takingthis refractive action into account.

FIG. 4 is a schematic illustrating the comparison of the optical pathsof the reflected light in the case where the reflecting film wasprovided on the inner surface of the auxiliary reflecting mirror and thecase where it was provided on the outer surface.

Referring to FIG. 4, the reference symbol 34 a stands for an ideal innersurface of the auxiliary reflecting mirror 30, and the actual innersurface 34 is assumed to be inclined at an angle θ with respect to thisideal inner surface 34 a. Furthermore, the reference symbol 50 standsfor a light source under an assumption that the center of thelight-emitting portion 11 is a point light source, 50′ stands for areflected light source in the case where the reflection was on the idealinner surface 34 a, 51 stands for a reflected light source in the casewhere the reflection was on the actual inner surface 34, and 52 standsfor a reflected light source in the case where the reflection was on theouter surface 33. Furthermore, R is the distance from the reflectedlight source 50′ to the ideal inner surface 34 a, and D is the tubularthickness of the auxiliary reflecting mirror 30. Further, n denotes therefractive index of the auxiliary reflecting mirror 30.

When the light 53 emitted from the light source 50 is reflected by theideal inner surface 34 a, the reflected light 53′ becomes the light thatpasses through the light source 50. Thus, because the reflected lightsource 50′ created by the reflected light 53′ that was reflected by theideal inner surface 34 a coincides with the light source 50, it willpass the same optical path as the light directly emitted from the lightsource 50 toward the main reflecting mirror 30. By contrast, in the caseof reflection on the inner surface 34 inclined with respect to the innersurface 34 a, because the inner surface 34 is inclined at an angle θ,the reflection angle θ1 becomes 2θ and the reflected light 54 isobtained. The displacement amount L1 of the reflected light source 51created by this reflected light 54 from the reflected light source 50′can be represented by the following formula (1).Displacement amount L 1=2(R·tan(θ1/2))  (1)

Furthermore, in the case of reflection on the outer surface 33, thelight beam angle of the light 53 emitted from the light source 50changes by 1/n·θ under the effect of the inclination of the innersurface 34 at the angle θ and the refractive index n of thelight-emitting tube 10, and the light becomes the light beam 53 a. Atthe time of reflection at the outer surface 33, the angle shifts by θ2(=2·1/n·θ) and the light becomes the reflected light 53 b. Further, whenthe reflected light 53 b passes through the inner surface 34, it isagain refracted by the angle 1/n·θ and eventually becomes a light beam53 c parallel to the light beam 53. The displacement amount of thereflected light source 52 created by this light beam 53 c from thereflected light source 50′ can be represented by the following formula(2).Displacement amount L 2=2(D·tan(θ2/2))  (2)

Here, it is assumed that the refractive index is 1.4602, the tubethickness D is 2 mm, and the distance R between the reflected lightsource 50′ and ideal inner surface 34 a is 10 mm. The reflection anglesθ1, θ2 of the reflected light on the reflecting surfaces and thedisplacement amounts L1, L2 from the reflected light source 50′ to thereflected light sources 51, 52, respectively, are calculated by usingthe above formulas (1) and (2) and changing the inclination angle θ ofthe actual inner surface 34 with respect to the ideal inner surface 34a. The graphs comparing the case where the reflection was on the innersurface 34 and the case where the reflection was on the outer surface 33are shown in FIG. 5. In FIG. 5, the inclination angle θ [degree] of theactual inner surface 34 with respect to the ideal inner surface 34 a isplotted against the abscissa, the reflection angle θ 1 or θ2 [ degree]of the reflected light at the inner surface 34 or outer surface 33 isplotted on the left ordinate. The displacement amount L1 or L2 [m] fromthe reflected light source 50′ to the reflected light source 51 or 52 isplotted against the right ordinate.

The symbol 61 in FIG. 5 stands for the reflection angle θ of thereflected light in the case of reflection on the inner surface 34, and62 stands for the reflection angle θ2 of the reflected light in the caseof reflection on the outer surface 33. The symbol 71 stands for thedisplacement amount L1 from the reflected light source 50′ to thereflected light source 51 in the case of reflection on the inner surface34, and the symbol 72 stands for the displacement amount L2 from thereflected light source 50′ to the reflected light source 52 in the caseof reflection on the outer surface 33. Here, θ1, θ2, L1, L2 correspondto θ1, θ2, L1, L2 shown in FIG. 4.

It is clear from FIG. 5, that at any inclination angle θ of the actualinner surface 34 with respect to the ideal inner surface 34 a, of thereflection on the inner surface 34 and the reflection on the outersurface 33, both the reflection angle of the reflected light and thedisplacement amount from the reflected light source 50′ to the reflectedlight source are smaller in the case of reflection on the outer surface33. It follows herefrom that when the inner surface 34 is inclined withrespect to the ideal inner surface 34 a, a higher light utilizationefficiency can be obtained with reflection on the outer surface 33.

FIG. 6 is a schematic of a projector equipped with the above-describedillumination device.

This projector 1000 includes an illumination optical system 300, a colorlight separation optical system 380, a relay optical system 390,liquid-crystal panels 410R, 410G, 410B, a cross dichroic prism 420, anda projection lens 600 which is a projection optical system.

The operation of the projector 1000 of the above-described configurationwill be described below.

The illumination optical system 300 is an integrator illuminationoptical system to almost uniformly illuminate the image formationregions of the liquid-crystal panels 410R, 410G, 410B and includes theillumination device 100 of the above-described exemplary embodiment, afirst lens array 320, a second lens array 340, a polarization conversionelement array 360, and a superposition lens 370.

First, the emitted light from behind the center of the light-emittingportion 11 of the light-emitting tube 10 is reflected by the mainreflecting mirror 20 frontward of the illumination device 100. Then, theemitted light from the zone in front of the center of the light-emittingportion 11 is reflected by the auxiliary reflecting mirror 30 andreturned to the main reflecting mirror 20. This light is then reflectedby the main reflecting mirror 20 frontward of the illumination device100. Here, because the reflecting surface 32 of the auxiliary reflectingmirror 30 is formed with good accuracy, as was described hereinabove,the incident light can be reflected with good efficiency toward the mainreflecting mirror 20. Further, the light outgoing from the illuminationdevice 100 enters the concave lens 200 and the propagation direction ofthe light is adjusted to be almost parallel to the optical axis of theillumination optical system 300.

The parallelized light falls on each small lens 321 of the first lensarray 320 and is split into a plurality of partial luminous fluxes whosenumber corresponds to the number of the small lenses 321. Furthermore,each partial luminous flux outgoing from the first lens array 320 fallson the second lens array 340 having small lenses 341 corresponding toeach respective small lens 321.

Further, the outgoing light from the second lens array 340 falls on thepolarization conversion element array 360 to adjust into linearlypolarized lights of the type with the same direction of polarization. Aplurality of partial luminous fluxes with the polarization directionadjusted with the polarization conversion element array 360 enter thesuperposition lens 370, where each partial luminous flux falling on theliquid-crystal panels 410R, 410G, 410B is adjusted so as to besuperimposed on the corresponding panel surface.

The light outgoing from the superposition lens 370 is reflected with thereflecting mirror 372 and then falls on the color light separationoptical system 380. The color light separation optical system 380 is anoptical system to separate the light emitted from the illuminationoptical system 300 into color lights of three colors: red, green, andblue and includes dichroic mirrors 382, 386 and a reflecting mirror 384.

The first dichroic mirror 382 transmits the red color light component ofthe light outgoing from the superposition lens 370 and reflects the bluecolor light component and green color light component. Further, the redcolor light component passes through the first dichroic mirror 382, isreflected by the reflecting mirror 384, and reaches the liquid-crystalpanel 410R for the red color light via a field lens 400R. Further, ofthe blue color light component and green color light component reflectedby the first dichroic mirror 382, the green color light component isreflected by the second dichroic mirror 386 and reaches theliquid-crystal panel 410G for the green color light via a field lens400G.

The blue color light component passes through the second dichroic mirror386 and falls on the relay optical system 390. The relay optical system390 is an optical system having a function of guiding the blue colorlight that passed through the dichroic mirror 386 of the color lightseparation optical system 380 to the liquid-crystal panel 410B andincludes an incoming-side lens 392, a relay lens 396, and reflectingmirrors 394, 398.

Thus, the blue color light component passes through the incoming-sidelens 392, reflecting mirror 394, relay lens 396, and reflecting mirror398 and then reaches the liquid-crystal panel 410B for the blue colorlight via a field lens 400B. Further, The relay optical system 390 isused for the blue color light in order to reduce or prevent the decreasein the light utilization efficiency caused by light scattering or thelike, resulting from the fact that the length of the optical path of theblue color light is larger than the length of the optical path of othercolor lights. Thus, the relay optical system serves to transmit thepartial luminous flux that fell on the incoming-side lens 392 directlyto the field lens 400B. Further, the relay optical system 390 has aconfiguration that transmits the blue color light of the three colorlights. But it may be also configured to transmit other color lights,for example, the red color light.

Then, the three liquid-crystal panels 410R, 410G, 410B modulate eachcolor light falling thereon according to the given image information andform the images of each color light. Further, polarizing plates areusually provided on the light incidence surface side and light outgoingsurface side of each liquid-crystal panel 410R, 410G, 410B.

Then, the modulated light of each color light outgoing from eachliquid-crystal panel 410R, 410G, 410B falls on the cross dichroic prism420 serving as a color light synthesizing optical system to synthesizethose modulated lights and forming a color image. In the cross dichroicprism 420, a dielectric multilayer film to reflect the red color lightand a dielectric multilayer film to reflect the blue color light areformed in an almost X-like fashion on the boundary surfaces of fourright prisms and the three color lights are synthesized by thosedielectric multilayer films.

Further, the color image outgoing from the cross dichroic prism 420 isenlarged and projected on a screen with the projection lens 600.

With the above-described projector 1000, because illumination device 100described hereinabove is provided, a high light utilization efficiencycan be obtained and an increased luminosity of the projector 1000 can beattained.

Further, the projector 1000 in accordance with an exemplary aspect ofthe present invention is not limited to the above-described exemplaryembodiment and can be implemented in a variety of modes, withoutdeparting from the essence thereof. For example, the followingmodifications are also possible.

In the above-described exemplary embodiment, there were used two lensarrays 320, 340 to split the light from the illumination device 100 intoa plurality of partial light fluxes. But the present invention can bealso applied to the projector which does not use such a lens array.

In the above-described exemplary embodiment, a projector usingtransmission-type liquid-crystal panels was described as an example. Butthe present invention is not limited thereto and can be also applied toa projector using reflection-type liquid-crystal panels. In the case ofa projector using reflection-type liquid-crystal panels, a configurationincluding only liquid-crystal panels is possible and a pair ofpolarizing plates are not required. Furthermore, in a projector usingreflection-type liquid-crystal panels, a cross dichroic prism issometimes used as a color light separation device to separate theillumination light into lights of three colors: red, green, and blue,and also as a color light synthesizing device to synthesize again themodulated lights of three colors and emitting them in the samedirection. Furthermore, sometimes a dichroic prism combining a pluralityof triangular or quadrangular rod-like dichroic prisms is used insteadof the cross dichroic prism. When the present invention is applied tothe projector using reflection-type liquid-crystal panels, it ispossible to obtain the effect almost identical to that obtained with theprojector using transmission-type liquid-crystal panels.

Further, the projector using three liquid-crystal panels as modulationdevices was explained as an example. However, the present invention canbe also applied to a projector with a structure using one, two, four ormore liquid-crystal panels.

Furthermore, the light modulation device to modulate the incident lightand generate an image is not limited to a liquid-crystal panel. Forexample, it may be also a device using a micromirror. Furthermore, thelamp device in accordance with an exemplary aspect of the presentinvention can be also employed in both the front projection-typeprojectors, in which image projection is conducted from the direction inwhich the projection surface is observed, and the rear projection-typeprojectors, in which image projection is conducted from the sideopposite to the direction in which the projection surface is observed.

INDUSTRIAL FIELD OF APPLICATIONS

An illumination device equipped with an exemplary aspect of theauxiliary reflecting mirror manufactured by the manufacturing method inaccordance with the present invention in the above-described manner canbe widely employed as a light source for a projector or other variousoptical devices.

1. A method for the manufacture of a reflecting mirror of anillumination device, including a light-emitting tube and the reflectingmirror to reflect a light from the light-emitting tube, the methodcomprising: heating a central portion of a quartz glass tube andcompressing the central portion by pushing two end portions of thequartz glass tube so that the wall thickness of the central portionthickens; accommodating the quartz glass tube after thickening the wallthickness of the central portion in a mold having an inner surfaceformed to a reflecting surface shape, which is to be formed in areflecting mirror, and forming an expanded portion by expanding thecentral portion, of which the wall thickness was thickened, byintroducing a gas from the two ends of the quartz glass tube; cuttingthe quartz glass tube in at least the central portion of the expandedportion; and evaporating a reflecting film on the outer surface of theexpanded portion and forming a reflecting surface.
 2. The method for themanufacture of a reflecting mirror according to claim 1, furthercomprising: cutting both end portions of cylindrical portions extendingoutwardly from the two ends of the expanded portion in addition tocutting the vicinity of the central portion of the expanded portion ofthe quartz glass tube, and providing cylindrical mounting supportportions to fix to the light-emitting tube.
 3. A reflecting mirrormanufactured by the method for the manufacture of a reflecting mirroraccording to claim
 1. 4. A reflecting mirror manufactured by the methodfor the manufacture of a reflecting mirror according to claim
 2. 5. Anillumination device, comprising: a light-emitting tube; and a reflectingmirror to reflect the light from the light-emitting tube toward anillumination region, the reflecting mirror being manufactured by themethod for the manufacture of a reflecting mirror according to claim 1.6. An illumination device, comprising: a light-emitting tube; and areflecting mirror to reflect the light from the light-emitting tubetoward an illumination region, the reflecting mirror being manufacturedby the method for the manufacture of a reflecting mirror according toclaim
 2. 7. An illumination device, comprising: a light-emitting tube; amain reflecting mirror to reflect the light from the light-emitting tubetoward an illumination region; and an auxiliary reflecting mirror toreflect the light from the light-emitting tube toward the mainreflecting mirror, the auxiliary reflecting mirror being manufactured bythe method for the manufacture of a reflecting mirror according toclaim
 1. 8. An illumination device, comprising: a light-emitting tube; amain reflecting mirror to reflect the light from the light-emitting tubetoward an illumination region; and an auxiliary reflecting mirror toreflect the light from the light-emitting tube toward the mainreflecting mirror, the auxiliary reflecting mirror being manufactured bythe method for the manufacture of a reflecting mirror according to claim2.
 9. A projector, comprising: the illumination device according toclaim 5, a light modulation device to modulate the luminous flux emittedfrom the illumination device according to an image information; and aprojection optical system to project the luminous flux modulated by thelight modulation device.
 10. A projector, comprising: the illuminationdevice according to claim 6, a light modulation device to modulate theluminous flux emitted from the illumination device according to an imageinformation; and a projection optical system to project the luminousflux modulated by the light modulation device.
 11. A projector,comprising: the illumination device according to claim 7, a lightmodulation device to modulate the luminous flux emitted from theillumination device according to an image information; and a projectionoptical system to project the luminous flux modulated by the lightmodulation device.
 12. A projector, comprising: the illumination deviceaccording to claim 8, a light modulation device to modulate the luminousflux emitted from the illumination device according to an imageinformation; and a projection optical system to project the luminousflux modulated by the light modulation device.